The present invention relates to a tire noise reducing system, more particularly to a noise damper for a pneumatic tire.
In recent years, as the mechanical noise from automobiles especially passenger cars is greatly reduced, the tires especially passenger car tires are strongly required to reduce their noise. There are many factors in the tire noise, but a circumferential resonance of the air in the annular tire cavity is a major factor. That is, a ring of air inside the tire continuous around the rim is excited by vibrations during running and resonates in the circumferential direction. Usually, a resonance peak occurs in a frequency range of from 50 to 400 Hz according to the tire size.
In the published Japanese patent JP-B-7-14682, an assembly of a wheel rim and a pneumatic tire mounted thereon is disclosed, wherein a ball-like body which is made of rubber, sponge or the like is put in the annular tire cavity to block the circumferential continuity thereof to control resonance.
In case of such a ball-like body, however, it has a tendency to make it difficult to mount the tire on a wheel rim.
It is therefore, an object of the present invention to provide a tire noise reducing system in which, by using a spongelike multi-cellular material having specific properties, the resonance noise is effectively reduced without hindering tire mounting operation.
According to the present invention, a tire noise reducing system comprises a wheel rim, a pneumatic tire to be mounted on the wheel rim and a noise damper to be disposed in an annular tire cavity enclosed by the wheel rim and the pneumatic tire mounted thereon, wherein the noise damper is made of multi-cellular material whose volume S2 is in a range of not less than 0.4% of the volume S1 of the annular tire cavity. Preferably, the specific gravity of the noise damper is in a range of from 0.005 to 0.06.
Here, the volume S1 of the tire cavity is defined by the following approximation expression
Axc3x97{(Dixe2x88x92Dr)/2+Dr}xc3x97pi 
wherein
A is the cross sectional area of the tire cavity under a standard state,
Di is the maximum outer diameter of the tire cavity under the standard state,
Dr is the diameter of the wheel rim, and
pi is the ratio of the circumference of a circle to its diameter.
The above-mentioned xe2x80x9cAxe2x80x9d and xe2x80x9cDixe2x80x9d can be easily obtained by CT scanning.
The standard state is that the tire is mounted on the wheel rim and inflated to a standard pressure but loaded with no tire load. The standard pressure is the xe2x80x9cmaximum air pressurexe2x80x9d specified in JATMA, the xe2x80x9cInflation Pressurexe2x80x9d in ETRTO, the maximum pressure given in the xe2x80x9cTire Load Limits at Various Cold Inflation Pressuresxe2x80x9d table in TandRA or the like. In case of passenger car tires, however, 200 kPa is used as the standard pressure.
The volume of the noise damper means the apparent volume of the spongelike multi-cellular material inclusive of the total volume of the cells under the above-mentioned standard pressure.